Electrodeposition of metals



Patented July 26, 1 938 UNITED STATES PATENT OFFICE ELECTRODEPOSITION 0FMETALS a corporation of Ohio No Drawing. Application October 21, 1936,Serial No. 106,816

11 Claims.

Various so-called addition agents have been proposed from time to timefor inclusion in nickel plating baths in order to control or affect thecharacter of the electrolytically deposited metal. One principalobjective in such modification of the plating bath has been to increasethe brightness or luster of the deposited metal, particularly wheredeposited as a plate on another metallic base. Such a bright nickelplate is not only desirable per se, but it is particularly advantageouswhere it is destined for use as the base for an electrolyticallydeposited chromium plate, since if the nickel plate does not requiretobe polished and buffed, a thinner plate gives the same protection asaheavier gray plate some of which must be taken off in polishing, andagain a very considerable saving in time and in cost in the productionof plated articles becomes possible, whether with nickel plate per se orwith additional chromium finish.

While it has long been known that the addition of certain substances tothe electrolytic plating bath will cause the nickel to be deposited as amore or less smooth, lustrous plate, with many such addition agents thecurrent density has to be kept very low, lower than desirable forcommercial usage. In many cases, also, the results tend to be variableor at least it is too diiiicult to maintain proper balance of theingredients in order to continuously plate out the nickel in the brightform desired.

Also, a tendency has been noted that the deposited nickel plate in someinstances, because of the presence of a film or an apparently passivestate perhaps, fails to take properly a bright superposed chromium platewhere the nickel is to serve as a base for the latter.

Among the objects of the present invention is the provision of a nickelplating bath and process which will produce superior bright ductilenickel plate under commercial conditions, i. e., wherein the currentdensity may be of commercial rate, with the plate deposited rapidly aswell as uniformly to any desired thickness and without pitting. Anotherobject is the provision of a plating bath and process capable ofindefinite operation, and exactness of control, as the condition of thebath can be ascertained instead of having to depend upon unknown andunascertainable colloidal conditions. A further object is the provisionof bright nickel plate in such manner as to insure the proper deposit ofa superposed bright chromium plate, if desired.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the composition of ingredients and steps hereinafterfully described and particularly pointed out in the claims, thefollowing description setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principle of the invention may beused.

We have discovered that the addition to a nickel plating bath of usualcomposition of an agent making available selenium or tellurium producesvery remarkable results, more especially in the brightening effect hadon the deposited plate. The surface of such deposited metal issurprisingly brilliant and mirror-like, even when the deposit isrelatively thick. Such bright nickel is obtainable even where thesurface of the underlying metal is dull, e. g., a steel surface.

The electrolytic bath as to its metal-providing components may be ofusual or desired composition, i. e., be a solution of so-called nickelsalts, for instance nickel sulphate with an admixture of a relativelysmaller amount of nickel chloride and a further small amount of boricacid. An-

other well known electrolyte comprises a solution of nickel sulphate andsodium sulphate with relatively small amounts of ammonium chloride andboric acid added.

The addition to any such electrolyte of a suitable selenium or telluriumcompound has the brightening effect above noted. The selenium ortellurium may be added in the form of acid compounds as S802, T602,HzSeOa, HzSeO4, salts of these acids, Na2SezO3, KCNSe, etc. or asorganic selenides or tellurides or organic selenium oxygen or telluriumoxygen compounds, as for instance organic seleninic acids, selenonicacids, (also salts thereof) selenols, and similar tellurium compounds.However, the organic compounds have in general been found less desirablethan the simpler inorganic forms because of difliculty of preparationand of odor or other unpleasant property. Selenic acid is particularlyadvantageous, as it dissolves in relatively high concentration and isnot critical in operating conditions, and will plate at a pH of 6,giving higher efflciency and less tendency for hydrogen co-deposit andbrittleness. In general, less selenium or tellurium will be required athigh pH to obtain brightness, and in practice the pH may range from 1.5to 6, or as limited by the bath itself, and the optimum may be asdesired in commercial practice, for instance generally 3.0 to 4.5. Thecurrent density rate may range as desired in practice from ten to onehundred fifty amperes per square foot in some cases and usually twentyto fifty amperes per square foot, and similarly, the effect ortemperature is not critical, the usual temperature ranges of fronr;30-to60 0., preferably around 50" C.,;iaeing applicable.

Where operating an electrolyte of low nickel concentration at lowcurrent density, a brightening efiect may be obtained with as little as0.001 per cent of SeOz or its equivalent selenium content. In moreconcentrated solutions, however, the amount may be up to 0.1 per cent,and for general purposes may range from 0.005 to 0.05 per cent fordesirable results. Similar concentrations of tellurium apply; within thelimits of solubility or dispersibility of its compounds.

Deposited plate where the foregoing selenium or tellurium compound aloneis added to the bath, while exceptionally bright, has a tendency to bebrittle. Furthermore, the bath tends to become depleted, by cathodicdeposition, ,of such agent at a rate which would militate against itsuse on ,a commercial scale. However, we have made the further importantdiscovery that both the foregoing objections are overcome or controlledby the addition of an agentwhich we find greatly decreases the amount ofselenium co-deposited with the nickel and in so doing increases thedue-- tility of the deposit, such agent being ;a sulphonate of anaromatic hydrocarbon. As for instance benzene sulphonates, naphthalenesulphonates, diphenyl sulphonates; sulphuric acid reaction products ofterpenes, etc. Thus we have found that naphthalene mono, di, and trisulphonates, mixtures of these, benzene disulphonate, diphenylsulphonates, etc., act particularly to control the rapidity with whichthe selenium or tellurium is co-deposited with the nickel and in thatconnection increasing the ductility of the deposit. Such agent wedesignate an agent for regulating the depletion of the {addition agent.In general, the amount of such control agent may range from 0.05 to 1per cent, but larger amounts up to a saturated solution may be used.

In the selection of a sulphonic acid suitable for this use it seems bestto choose those which are as free as possible from colloidal organicmaterial present as impurities formed during the sulphonation, which hasa brightening and embrittling eifect on the deposited nickel. i The puresulphonates or commercial mixtures 05 sulphonates: suitable for use inthe bath contribute very little to the brightness'of the plate and whenused in the plating bath without addition of a selenium or telluriumcompound produce a gray ductile plate. The deposit or" nickel obtainedwhen a selenium or teliurium compound is added to such a bath dsmirror-bright and ductile. However,;if an impure-sulphonate containingdispersed er colloidal organic material be used which produces a brightplate itself, the addition of azselenium or tellurium compound may causeextreme brittleness.

Where a sulphonate as above mentioned is thus added along with aselenium or tellurium compound as specified, the deposited plate isfound to be not only brilliantly mirror-like and free from milky-graycloudiness, when deposited on a relatively smooth surface, but it alsotends to level up and deposits brilliantly omunpolished surfaces and canbe built up as thickly as desired. The deposit on analysis shows acontent of selenium or tellurium, w d'iichever such agent is used,together with a content of sulphur derived from the sulphurhontainingradical of the organic addition agent. The amount of sulphur thuscodep'nsited with the nickel will vary from a trace to several tenths ofone per cent, usually from 0.01 to 0.1 per cent, depending upon theamount and kind of the organic agent employed in the bath. The amount ofselenium or tellurium codeposited with the nickel will vary from a traceto several per cent, usually from 0.01 to 1 per cent;

depending upon the composition of the bath, the

tained less than .001 sulphur and 1.6 per cent, selenium and althoughbright was extrenj ely brittle.

In'general; we find 0.01 to 0.1 per cent of sulphur and 0.05 to 0.6 percent of selenium (or corresponding amount of tellurium) in plates ofproper brightness with ductility. We find also that by including in theelectrolytic bath a substance or agent which lowers the surface tensiona still better result is obtained. We have found sulphated higheralcohols of six or preferably eight or more carbon atoms, on up to abouttwenty, as for instance sulphated laufryl, oleyl, octy1, caprylic,cetyiic alcohols, etc., particularly advantageous for this in a bathwhich includes the above mentioned addition agents. Such agent wedesignate a surface-tension reducing agent. The criterion governing theamount of such latter agent to be added to the bath is afforded by thesurface tension which may be determined by a suitable means,conveniently ior instance the Jaeger tensimeter, as described inAdvanced Practical Physics for Students by B. A. Warnop and H. T. pages-143, (pub. by Methuen, London, 1927). Thus, where the bath wouldlllIlFfOI example, on the order of 60-70 dynes per centimeter as thusdetermined, it should be adjusted with the sulphated alcohol or the liketo not in excess of 50 dynes per centimeter, and preferably below 40; 2

The following will serve as illustrative examples of our improved nickelplating bath utilizing one or more of the abo e described additionagents: 1

Oz. per gal. I. NiSO4,6HzO 32 NiC12,5H2O 4 HzBOs 5 pH may be about 4.0,and the temperature 30-60 C. V II. With similar amounts of nickel saltsand boric acid as in Ex. I there is incorporated W SeOz 0. 01

Naphthalene di-sulphonic acid 1 Witli similar amounts of nickel saltsand boric acid as in Ex. I there is incorporated TeOz 0. 025 IV. Withsimilar amounts of nickel salts and boric acid as in Ex. I there isincorporated S802 i 0. 01 Naphthalene di-sulphonic acid 1 and laurylalcohol sulphate 0.1 V. With similar amounts of nickel salts andboricacid as in Ex. I there is incorporated l SeOz 5 0. 01 Benzenedi-sulphonic acidi. 1 and octyl alcohol sulphate 0. 2

araaaao 3 Oz. per gal. with the condition encountered where our newlyVI. With similar amounts of nickel salts discovered brightening agent isemployed.

and boric acid as in Ex. I there is For example, cathodic cleaning in 'aregular incorporated cleaning solution containing borax iseffective inTeoz 0.02 some cases, especially if a small amount of glu-Alpha-naphthalene sulphonic-acid- 0. 2 co'se or sugar be added, but notinfrequently the Lauryl alcohol sulphate 0. 1 film condition appears tobe of such a thickness VII. With similar amounts of nickel salts thatcleaning in this manner cannot be effected and boric acid as in Ex. Ithere is in any reasonable length of time. incorporated We also havetried adding copper cyanide to $602 0.01 the cleaner, depositing a filmof copper and re- 3 oz. per gal. of a water solution of moving such filmwith chromic acid either in the a nickel-neutralized product of chromicacid bath or by a pretreatment, as well the action of 2 parts of 20 peras plating on a film of zinc and stripping this cent oleum on 1 part ofnaphthawith hydrochloric acid. Here again the cleaning lene at 160 C.for 2 hours, the is ineffective if the film condition is bad.nickel-neutralized solution being We have found, however, that by thefollowing of such concentration as to be procedure the nickel plate canbe quickly and equivalent to Bper cent naphthaeffectively put incondition for the superposed lene, and additionally there is chromiumplate, viz., by placing the nickel plated incorporated lauryl alcoholsularticle in a solution of sodium cyanide, and then phate 0. 1 usingthe metal plated article as an anode, pass- VIII. NiSO4,6HzO 32 ing anelectric current therethrough at a voltage NiCl2,6H2O 4: o ro 2 to 10volts for a period of about 1 H 30 5 second; we then reverse the currentmaking the Selenic acid 0.1 a piece athode for a few seconds up toseveral IX. With similar amounts of nickel salts minutes. There is nodefinite time limit for such and boric acid as in Ex. I there is lastmentioned step (cathodic treatment), but incorporated ordinarily 15-30seconds will be quite suificient. Selenlc acid 0.1 A suitable sodiumcyanide solution will contain 23 Naphthalene di-sulphonic acid 1 ouncesper gallon and the solution may be used X. With similar amounts ofnickel salts at room temperature or warm, as desired.

and boric acid as in Ex. I there is We find that by making the pieceanode in a incorporated sodium cyanide solution, the objectionable filmSelenic acid 0.1 effect is removed, but apparently the nickel sur-Naphthalene di-sulphonic acid 1 face is left passive. However, by makingthe piece and lauryl alcohol sulphate 1 first anode and then cathode,the surface film XI. With similar amounts of nickel salts is q y pp d ge nodic treatand boric acid as in Ex. I there is ment and the surface ofthe metal then reactiincorporated vated by the cathodic treatment. Wherethe Selenic acid 0.1 shapes are very complicated, it may be necessaryBenzene di-sulphonic acid, 1 to continue the anodic treatment for aslong as and octyl alcohol sulphate 0, 2 or even seconds before reversingthe current XII. With similar amounts of nickel salts and subjecting tothe cathodic treatment.

and boric acid as i 1 th is Where the foregoing cleaning procedure isfolincorporated lowed, the chromium covers exceptionally well Selenicacid o. 1 and it should be noted that such procedure is not 3 per of awater Solution f necessarily limited to the treatment of bright anickepneutralized product of nickel plate produced with our improvedaddit action of zparts of 20 per t; tion agents, but is found highlybeneficial in oleum on 1 part of naphthalene cleaning nickel plateproduced from the regular t 1 0 for 2 hours, t i k lplating bath andthen buffed as a preliminary neutralized solution being of such step tchromium P concentration as t b equivalent, In place of using a cleaningsolution containing t 3 per c t aphth l e, a d simply sodium cyanide, asspecified above, we additionally there is incorporated may substitutesoda ash in part for such sodium lauryl h l 5u1phate 0,1 cyanide andseemingly obtain results that are x111. With similar amounts of nickelsalts t about s good- An example of such modified d b ri a id as i x, 1there 1 solution would comprise approximately 4 ounces incorpgrated ofsodium cyanide and 4 ounces of soda ash to a KCNse 0 05 gallon of water.We have also found that sodium Alphamaphthalene sulphomc acid 0 2formate can be substituted in large part for the Octyl alcohol sulphate0, 2 s ium cy nid and t t a good cleaning bat-h can v In t such as 1Xthere is be had using only 1 or 2 ounces of sodium cyanide incorp'omtedethyl 1 1d 0 03 to 6 or 7 ounces of sodium formate per gallon of insteadof the KCNSe.

Where another metal is to be superposed on the bright nickel platedeposited from our improved composition of bath, as for example wherechromium is to be plated over the nickel by the usual process, whilevarious more or less familiar methods of cleaning of the plated surfacehave been heretofore employed, none of these have been whollysatisfactory, particularly in dealing water. In the case of each of thenamed ingredients, or combination of ingredients, for the cleaningsolution, it may be desirable to increase the conductivity of the latterby the addition of conducting salts. This would be more especially thecase where the nickel plated article to be cleaned is of complicatedshape, such as a radiator shell or the like.

We have also found that in place of subjecting the article first toanodic and then to cathodic treatment, satisfactory results can also beobtained by using an alternating current superimposed upon a directcurrent so as to obtain a cathode efiect in excess of the anode efiect.This, however, requires a somewhat more elaborate electrical set-up thansimple current reversal, which we regard as providing the more practicalprocedure.

By following the steps of the process hereinbefore described, includingthe addition -to a nickel plating bath of a selenium or telluriumcompound, an organic sulphonate as noted as a regulating agent and asurface tension reducing agent, preferably a sulphated higher alcohol asindicated to avoid pitting, a very superior bright nickel plate isobtained which possesses not only the desired characteristic ofbrilliant smoothness, but which can be built up to any desired thicknessand is free from brittleness, i. e., is surprisingly ductile, so thatthe plated article can be bent without any evidence of crackling.Furthermore, the bright nickel plated articles thus produced, even whereof intricate design, will, when cleaned in accordance with the preferredprocedure described above and further subjected to the standard chromicacid chromium plating process, take a superposed chromium plateperfectly.

This application is a continuation, in part and as to common subjectmatter, of our application Serial No. 74,340, filed April 14, 1936.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims, or the equivalent ofsuch, be employed.

We therefore particularly point out and distinctly claim as ourinvention:

1. An electro-deposition bath, comprising an acid nickel electrolyte andan amount of a brightening addition agent selected from the groupconsisting of compounds of selenium and tellurium, soluble in theelectrolyte, sufficient to produce a brilliant but normally brittledeposit and an amount of an aromatic sulphonate suificient to counteractthe normal embrittling efiect of said brightener compound and to renderthe deposit ductile.

2. An electro-deposition bath, comprising an acid nickel electrolyte andan amount of selenium compound brightening addition agent, soluble inthe bath, sufiicient to produce a brilliant but normally brittle depositand an amount of a benzene sulphonate suflicient to counteract thenormal embrittling efi'ect of said brightener compound and to render thedeposit ductile.

3. An electro-deposition bath, comprising an acid nickel electrolyte andan amount of selenium compound brightening addition agent, soluble inthe bath, suflicient to produce a brilliant but normally brittle depositand an amount of a naphthalene sulphonate sufficient to counteract thenormal embrittling efiect of said brightener compound and to render thedeposit ductile.

4. An electro-deposition bath, comprising an acid nickel electrolyte andan amount of selenium compound brightening addition agent, soluble inthe bath, suiiicient to produce a brilliant but normally brittle depositand an amount of a naphthalene disulphonate sufficient to counteract thenormal embrittling effect of said brightener compound and to render thedeposit ductile.

5. An electro-deposition bath, comprising an acid nickel electrolyte andan amount of selenium compound brightening addition agent, soluble inthe bath, sufiicient to produce a brilliant but normally brittle depositand an amount of a mixture of naphthalene mono, diand tri-sulphonatessufllcient to counteract the normal embrittling efiect of saidbrightener compound and to render the deposit ductile.

6. An electro-deposition bath, comprising an acid nickel electrolyte towhich there has been added an amount of selenium dioxide sufiicient .toproduce a brilliant but normally brittle deposit,

an amount of a naphthalene sulphonate material containing a naphthalenedi-sulphonate sufficient to counteract the normal embrittling effect ofsaid brightener compound and to render the deposit ductile and a minoramount of a sulphate of an aliphatic alcohol having from eight to twentycarbon atoms in the molecule.

7. An electro-depositi'on bath comprising an acid nickel electrolytecontaining as a brightening addition agent an amount'of a seleniumcompound, soluble in the electrolyte, equivalent to the addition of fromabout 0.001% to about 0.10% of selenium dioxide and an amount of anaphthalene sulphonate in excess of about 0.05% and suflicient tocounteract the embrittling efi'ect of the amount of selenium compoundpresent in the bath and render the deposit ductile.

8. The process of electro-depositing nickel in brilliant and ductileform from an acid nickel electrolyte containing an amount of abrightening addition agent selected from the group consisting ofcompounds of selenium and tellurium, soluble in the electrolyte,sufiicient to produce a brilliant but normally brittle deposit and anamount of an aromatic sulphonate sufiicient to counteract the normalembrittling efiect of said brightener compound and to render the depositductile.

9. The process of electro-depositing nickel in brilliant and ductileform from an acid nickel electrolyte containing in solution an amount ofselenium compoundbrightening addition agent suflicient to produce abrilliant but normally brittle deposit and an amount of a benzenesulphonate suflicient to counteract the normal embrittling efiect ofsaid brightener compound and to render the deposit ductile.

10. The process of electro-depositing nickel in brilliant and ductileform from an acid nickel electrolyte containing in solution an amount ofselenium compound brightening addition agent suflicient to produce abrilliant but normally brittle deposit and an amount of a naphthalenesulphonate sufllcient to counteract the normal embrittling efiect ofsaid brightener compound and to render the deposit ductile.

11. The process'of electro-depositing nickel in brilliant and ductileform from an acid nickel electrolyte containing in solution an'amount ofselenium compound brightening addition agent suflicient to produce abrilliant but normally brittle deposit and an amount of a naphthalenedi-sulphonate suificient to counteract the normal embrittling efiect of"said brightener compound and to render the deposit ductile.

WILLIAM J. HARSHAW. KENNETH E. LONG.

